PMI support for DS-Lite tunnel

Enhance DS-Lite tunnel performance by reducing instruction cache misses and optimizing the packet processing path. Use Packet Management Interface (PMI) for DS-Lite  tunnel processing, which includes encapsulate IPv4 packets within an IPv6 header using Vector Packet Processing (VPP), decapsulate by stripping the IPv6 header to process the inner IPv4 packet, and handling post-fragmentation of DS-Lite encapsulated traffic if it exceeds the tunnel's Maximum Transmission Unit (MTU).